US golf star Tiger Woods says he is upbeat about regaining the world number-one spot with three events remaining this year, starting with this week's HSBC Champions tournament in Shanghai.

US golf star Tiger Woods says he is upbeat about regaining the world number-one spot with three events remaining this year, starting with this week's HSBC Champions tournament in Shanghai.

"As far as the world ranking is concerned, yes, I'm not ranked No. 1 in the world," Woods said after beating Japanese star Ryo Ishikawa in a nine-hole made-for-television exhibition match in Yokohama near Tokyo.

"In order to do that you have to win, and I didn't win this year," he told media on Monday when his world ranking was confirmed to have slipped behind Englishman Lee Westwood after 281 weeks, or more than five years, at the top.

But the 34-year-old could still regain the highest ranking at the World Golf Championship event which starts on Thursday at Sheshan International golf club in Shanghai, where American Phil Mickelson will be the defending champion.

"I've got three more events this year and, hopefully, I can end on a good note," he said, according to TigerWoods.com. "I'm really looking forward to these events and, hopefully, they will spearhead into a better 2011."

The 14-times Major winner's seemingly well-ordered life was thrown into turmoil by revelations of extra-marital affairs that led to the collapse of his marriage and a five-month break from the game.

He has only two top-five finishes in his last 12 PGA Tour events and is now ranked just above PGA champion Martin Kaymer of Germany, Mickelson and another American, Steve Stricker.